Smooth plasma etching of GeSn nanowires for gate-all-around field effect transistors

Abstract

We report on the nanopatterning of horizontal and vertical germanium-tin (Ge1−x Sn x or GeSn) nanowires by inductively coupled plasma reactive ion etching for gate-all-around field effect transistors. First, a chlorine based chemistry has been investigated and optimal conditions identified for GeSn 6% alloys. Then, plasma etching was optimized to etch high Sn content GeSn alloys (up to 15%) with a high anisotropy, smooth sidewalls and a high selectivity versus a hydrogen silsesquioxane hard mask. We have shown that, in order to obtain smooth surfaces after plasma etching, a HCl pre-treatment was mandatory to eliminate the native Sn and Ge oxides. This behavior was even more pronounced for high Sn contents. Finally, we succeeded in patterning 20 nm wide suspended beams from GeSn layers with Sn concentrations up to 15%.